A Cloudy Target: Europe's Venus Express Probe to Explore Shrouded Planet
An artist's interpretation of the European Space Agency's (ESA) Venus Express spacecraft orbiting the second planet in our Solar System.
Credit: ESA.

Despite a delayed start, Europe's first Venus probe is preparing to launch spaceward on a mission to study the planet's soupy atmosphere and, hopefully, answer many of the nagging questions raised by past expeditions to the cloudy world.

While an insulation contamination problem prevented today's planned launch of the European Space Agency's (ESA) Venus Express probe, inspections of the spacecraft and booster are underway, ESA officials said Tuesday.

The spacecraft is in "good status" and engineers are confident they will have the probe ready to launch from Baikonur Cosmodrome, Kazakhstan atop a Soyuz-Fregat rocket before its flight window closes on Nov. 24, they added.

Venus Express is expected to fly the first dedicated mission to Venus in 25 years following NASA's Magellan spacecraft in 1989, and is the ESA's second swiftly-built non-Earth orbiter to bear the name "Express." Its predecessor, Mars Express, is currently circling the red planet.

"The science from these two missions will help to understand our place here," Venus Express project manager Don McCoy, who also worked on the Mars Express spacecraft, told SPACE.com in an e-mail interview.

Many of the orbiter's seven instruments were derived from the ESA's Mars Express and comet-bound Rosetta spacecraft, which eased development costs and scheduling, making it the space agency's fastest-built science satellite to date.

"Clearly, the availability of existing spare instruments from Rosetta and mars Express allowed us to shorten the usual development time for a scientific satellite," McCoy said.

The $226 million (220 million Euro) mission is expected to arrive at Venus in April 2006, he added.

Understanding Venus

Unlike the Magellan probe, which used radar to generate a surface map, Venus Express has its sights set on the planet's thick, turbulent and toxic atmosphere.

"Venus Express does not have the same mission as Magellan, aside from the clear objective of studying Venus," McCoy said. "[Ours] is an orbiter designed to study the atmosphere globally over a long period, whereas Magellan was designed to study the surface."

Among other things, researchers hope to understand what role the "greenhouse effect" of trapped carbon dioxide, water vapor and sulphuric aerosols gases played in the heating of Venus' atmosphere to its current average surface temperature of about 869 degrees Fahrenheit (465 degree Celsius).

To perform its mission, Venus Express carries three spectrometers, one magnetometer, a high-resolution camera, radio tools and a plasma-watching instrument dubbed ASPERA similar to one aboard Mars Express.

"A good deal of the time and effort of scientific satellites are spent in the development of very specialized instruments," McCoy said. "When a spare can be taken, with a few modifications to tune it to a new mission, there is a clear advantage of time and money."

The spacecraft's Planetary Fourier Spectrometer - also legacy instrument from Mars Express - will record the temperature of Venus' atmosphere all the way down to the surface, where researchers hope the instrument may be able to search for volcanic activity.

"It would be great to discover an active volcano and to prove that the planet still is active geologically," said H?kan Svedhem, Venus Express project scientist, in an ESA interview.

Venus Express does sport two almost wholly originally instruments. The probe's Venus Express Magnetometer and Venus Monitoring Camera - the high-resolution imager - were built specifically for their mission, ESA officials said.

Spacecraft engineers reused a Rosetta sensor design for the magnetometer and a few leftover parts from the Mars probe's High-Resolution Stereo Camera.

"In principle, it was necessary to resist changes as much as possible to avoid schedule and cost impacts," McCoy said, adding that his team did embrace change "aggressively" where necessary. "The experiences on Mars Express were definitely an asset in this balance because the knowledge...could be applied directly from one satellite to the next."

A different planetary express

While ESA officials have billed the 2,799-pound (1,270-kilogram) Venus Express as a near-twin of its Mars-watching counterpart, the spacecraft is much more than a mere clone.

Because the Venusian environment differs substantially from that of Mars due to its location closer to the Sun, engineers modified the heat insulation covering Venus Express' 5-foot by 6-foot by 4.5 foot (1.5-meter by 1.8-meter by 1.4-meter) exterior to survive higher temperatures and radiation levels.

Temperatures around Venus are four times higher than those experienced by Mars Express, prompting engineers to rearrange their orbiter's 23 layers of insulation and swath them in gold - as to the black used on the Mars probe - to reflect sunlight, and enlarged the spacecraft's radiators to handle the additional heat, ESA officials said.

Spacecraft designers were also able to shed some weight by decreasing the size of Venus Express' two wing-like solar panels.

Because the spacecraft will be flying much closer to the Sun than Mars Express sunlight appears twice as powerful, allowing the probe to rely on about 64 square feet (six square meters) of solar cells, which are also more heat-tolerant than those used aboard the Mars orbiter, ESA officials said.

But that weight savings was offset by the need for added propellant due to additional gravitational forces Venus Express will have to fend off to maintain an orbit around its target planet.

Venus' gravitational pull is almost as strong as Earth's and about eight times that of Mars, ESA officials said. That added gravity, plus the added pull of the Sun, required engineers to pack about 20 percent more fuel aboard Venus Express, they added.

When fully fueled, Venus Express is designed to carry 1,256 pounds (570 kilograms) of fuel - almost half the probe's total mass - into space.

A two-day mission (on Venus, that is)

While Venus Express is expected to spend about 15 months studying its cloud-covered target, the mission will span only two of the world's exceedingly long days.

"We use the Venus sidereal day, [about] 243 Earth days, as a convenient measure of mission duration," McCoy said, adding that Venus Express is prepared a mission extension should it be needed. "The satellite carries sufficient reserves for an extension of another two Venus days if the health is adequate, but this will be decided later in the mission."

Before Venus Express' mission managers can even think about beginning science operations around Venus - let alone extending the spaceflight - they must first launch the orbiter into space. ESA officials are confident that engineers will be able to clean up the insulation contamination and again prepare the spacecraft for flight before its launch window closes on Nov. 24.

"The Soyuz rocket we are using has a very good record so I am very hopeful that it will work out well," Svedhem said before the current contamination hitch.

But the launch delay hasn't dampened the excitement for McCoy, who feels Venus Express will link him - robotically, at least - to another world.

"I find I'm drawn to look at the sky more than usual," McCoy said, adding that both Venus and Mars are clearly visible in the night sky at Baikonur Cosmodrome. "It is magical to stand on one planet and feel connected to two other planets in the skies overhead in such a manner."